1. Field of the Invention
This invention relates to a polyimide silicone resin especially less containing volatile cyclic siloxane oligomers, a process for its production, and a polyimide silicone resin composition comprised of it as an effective component and having a good adhesiveness (bond strength).
2. Description of the Prior Art
Polyimide resins are commonly used as materials for printed circuit boards and heat-resistant adhesive tapes because of their high heat resistance and superior electrical insulation properties. Although the polyimide resins are used as resin varnish to form surface protective films and interlayer insulating films of electronic parts and semiconductor materials, they are capable of dissolving only in limited solvents. Accordingly, a method is commonly employed in which a solution prepared by dissolving in an organic solvent a polyimide precursor polyamic acid capable of relatively readily dissolving in various organic solvents is coated on a substrate, followed by removal of the solvent and then high-temperature treatment to effect dehydration cyclization and the product obtained is used as polyimide resin. Also, in order to, e.g., improve the solubility of polyimide resin in solvents, improve its adhesive force to substrates and impart flexibility, it is popular to introduce a siloxane chain into the polyimide skeleton. Siloxane materials widely used to introduce a siloxane chain into the polyimide skeleton are diaminosiloxanes, i.e., straight-chain silicones having amino groups at both terminals.
However, diaminosiloxanes which are commonly available contain cyclic siloxanes as impurities. Some cyclic siloxanes are volatile, and such volatile siloxanes are known to cause trouble in electrical contacts of relays, switches, motors and so forth used in electronic and electrical equipment. Also, as is seen from the fact that siloxanes are used as release agents (parting agents), they have had a problem that the presence of cyclic siloxanes in polyimide silicones may lower the adhesiveness or bond strength to substrates.
Meanwhile, electronic and electrical equipment or semiconductor chips are increasingly made compact or made high-performance. Accordingly, it is long-awaited to provide a polyimide silicone resin or polyimide silicone resin composition having a high reliability and a high adhesiveness.
Under such circumstances, an object of the present invention is to provide a polyimide silicone resin made to less contain the cyclic siloxane oligomers causative of the trouble in electrical contacts, a process for its production, and a polyimide silicone resin composition comprised of such a resin as an effective component and showing a good adhesiveness (bond strength) to substrates and a high reliability.
As a result of extensive studies made in order to solve the problems discussed above, the present inventors have discovered that a polyimide silicone resin less containing cyclic siloxane oligomers and having a relatively low glass transition point and a composition containing this resin as an effective component can solve the problems. They have also discovered that the polyimide silicone resin less containing cyclic siloxane oligomers can be obtained by using as a diamine component a diaminosiloxane less containing cyclic siloxane oligomers. Thus, they have accomplished the present invention.
More specifically, the present invention in the first aspect provides a polyimide silicone resin which contains not more than 300 ppm of a cyclic siloxane oligomer having 10 or less silicon atoms, has a glass transition point of 250xc2x0 C. or below and is soluble in an organic solvent.
The present invention in the second aspect provides a process for producing a polyimide silicone resin from a tetracarboxylic dianhydride and a diamine, wherein the diamine contains a diaminosiloxane represented by the following general formula (10), and the diaminosiloxane contains not more than 300 ppm of a cyclic siloxane oligomer having 10 or less silicon atoms. 
wherein n represents an integer of from 0 to 120, and R1 and R2 each represent an alkyl group having 1 to 8 carbon atoms or a phenyl group.
The present invention also in the third aspect provides a polyimide silicone resin composition comprising from 50% by mass to 99% by mass of the above polyimide silicone resin and from 1% by mass to 50% by mass of an epoxy compound.
The present invention will be described below in detail.
In the polyimide silicone resin of the present invention, a cyclic siloxane oligomer having 10 or less silicon atoms is kept in a small content.
In the present invention, the cyclic siloxane oligomer having 10 or less silicon atoms may include, for example, compounds represented by the following general formula:
(R3R4SiO)m 
wherein R3 and R4 may be the same or different and each represent an alkyl group having 1 to 8 carbon atoms or a phenyl group, the alkyl group including e.g., a methyl group, an ethyl group or a propyl group; and m is an integer of 3 to 10; and may specifically include hexamethylcyclotrisiloxane and octamethylcyclotrisiloxane. Any of these cyclic siloxane oligomer in the polyimide silicone resin must be in a content not more than 300 ppm in order to materialize a high reliability and a high adhesive performance. It may more preferably be in a content of 100 ppm or less.
The polyimide silicone resin of the present invention may also preferably have not so high glass transition point in order to materialize a good adhesiveness or bond strength. It may have a glass transition point of 250xc2x0 C. or below, and more preferably from 50xc2x0 C. to 200xc2x0 C.
When the polyimide silicone resin of the present invention is used as a component of adhesives, it is dissolved in an organic solvent to prepare them, and hence must be soluble in the organic solvent.
The organic solvent used here may include polar solvents such as N-methyl-2-pyrrolidone, cyclohexanone, N,N-dimethylformamide and N,N-dimethylacetamide, ketone type solvents such as 2-butanone and 4-methyl-2-pentanone, and ether type solvents such as tetrahydrofuran and propylene glycol dimethyl ether.
As methods for making the content of the cyclic siloxane oligomer small in the polyimide silicone resin, known methods may be used, which may include, e.g., a method in which the polyimide silicone resin is once dissolved in a solvent and thereafter re-precipitated to take out the polyimide silicone resin to bring the cyclic siloxane oligomer into a small content, and a method in which a siloxane originally having the cyclic siloxane oligomer in a small content is used as a material. In particular, the method in which a siloxane originally having the cyclic siloxane oligomer in a small content is used as a material is desirable from the viewpoint of saving of natural resources and power saving.
As this siloxane material, it is preferable to use the diaminosiloxane represented by the general formula (10). In this diaminosiloxane, the cyclic siloxane oligomer may preferably be in a content not more than 300 ppm, and more preferably not more than 100 ppm. As methods for making the content of the cyclic siloxane oligomer small in the diaminosiloxane, known methods may be used, which may include, e.g., methods such as striping at high temperature and extraction making use of a solvent. In the general formula (10), n represents an integer of from 0 to 120, and R1 and R2each represent an alkyl group having 1 to 8 carbon atoms or a phenyl group.
As the above polyimide silicone resin, it is preferable to use a polyimide silicone resin having repeating units represented by the following general formulas (a) and (b). 
In the formulas;
X is at least one organic group selected from tetravalent organic groups represented by the formulas (1), (2) and (3): 
Y is an organic group selected from i) a divalent organic group represented by the general formula (4): 
where B is at least one organic group selected from organic groups represented by the formulas (5), (6) and (7): 
and ii) a divalent organic group represented by the general formula (8): 
where D is at least one organic group selected from a single bond, xe2x80x94CH2xe2x80x94, xe2x80x94(CH3)2Cxe2x80x94,xe2x80x94SO2xe2x80x94 and xe2x80x94(CF3)2Cxe2x80x94; and
Z is a divalent siloxane residual group represented by the general formula (9): 
where R is a methyl group or a phenyl group, and b is an integer of 0 to 120.
The polyimide silicone resin is produced by a known process and from a tetracarboxylic dianhydride and a diamine containing the diaminosiloxane represented by the general formula (10). The diaminosiloxane represented by the general formula (10) may be used in an amount of from 5 to 75 mol %, and preferably from 10 to 50 mol %, of the total diamine. Also, as a diamine other than the diaminosiloxane represented by the general formula (10), it may preferably include a diamine which provides residual groups exemplified as the groups of the above general formulas (4) and (8).
A preferred process for producing the polyimide silicone resin is described below.
For example, at least one tetracarboxylic dianhydride selected from 2,2-bis-(3,4-benzenedicarboxylic anhydride)perfluoropropane, represented by the formula (11), and bis- (3,4-dicarboxyphenyl)-sulfone dianhydride, represented by the formula (12): 
at least one hydroxyl-group-containing aromatic diamine selected from aromatic diamines having phenolic hydroxyl groups represented by the formulas (13), (14) and (15): 
at least one diamine component selected from an aromatic diamine represented by the formula (16), a fluorine-containing aromatic diamine represented by the formula (17) and an aromatic diamine represented by the formula (18): 
at least one diaminosiloxane represented by said general formula (10) wherein n is an integer of 0 to 120, and R1 and R2 each represent an alkyl group with 1 to 8 carbon atoms or a phenyl group, are charged into a solvent such as cyclohexanone to allow them to react at a low temperature, i.e., about 20 to 50xc2x0 C. to synthesize polyamic acid silicone which is a precursor of the polyimide silicone resin.
Here, the proportion of the diamine component to the tetracarboxylic dianhydride component may appropriately be determined in accordance with, e.g., the modifying of molecular weight of the polyimide silicone resin, and may usually be in the range of from 0.95 to 1.05, and preferably from 0.98 to 1.02, in molar ratio. To modify the molecular weight of the polyimide silicone resin, a monofunctional material such as phthalic anhydride or aniline may be added. In such a case, the material may preferably be added in an amount of 2 mol % or less based on the weight of the polyimide silicone resin.
Subsequently, the resultant polyamic acid silicone solution is heated to a temperature usually in the range of from 80 to 200xc2x0 C., and preferably from 140 to 180xc2x0 C., to cause the acid amide moiety of the polyamic acid silicone to undergo dehydration cyclization reaction to obtain the polyimide silicone resin in the form of a solution. Another method is also available in which an acetic anhydride/pyridine mixture solution is added to the polyamic acid silicone solution and then the resultant solution is heated to about 50xc2x0 C. to effect imidization.
The polyimide silicone resin composition of the present invention is comprised of i) the polyimide silicone resin which contains not more than 300 ppm of the cyclic siloxane oligomer having 10 or less silicon atoms, has a glass transition point of 250xc2x0 C. or below and is soluble in an organic solvent, and ii) 1 to 50% by mass of an epoxy compound mixed in 50 to 99% by mass of the former. If the epoxy compound is mixed in an amount more than 50% by mass, the features of polyimide silicone may be damaged. A catalyst may also be added in order to accelerate the reaction of the epoxy compound. As the catalyst, usable are known catalysts such as imidazoles, amines and acid anhydrides. Also, as the epoxy compound, any known epoxy resin may be used. For example, the epoxy resin may include, as effective ones, bifunctional epoxy compounds such as bisphenol-A types and bisphenol-F types, and besides polyfunctional epoxy compounds having three or more functional groups.
The polyimide silicone resin of the present invention, unlike the polyamic acid type, does not require any long-time heating at such a high temperature of 250xc2x0 C. or above for its imidization. Also, since this polyimide silicone resin has been made to less contain the volatile cyclic siloxane oligomers which may lower adhesiveness and are causative of the trouble in electrical contacts, it is suited for uses where a high reliability is required, such as electronic and electrical equipment or semiconductor chips, and is suitable as, e.g., adhesives or coating materials for devices. The polyimide silicone resin composition having this polyimide silicone resin as an effective component also has a good adhesiveness or bond strength to substrates, and is suitable as adhesives or coating materials. Moreover, the polyimide silicone resin or the polyimide silicone resin composition can be made into films by coating on substrates the resin or composition dissolved in a solvent, evaporating the solvent off and peeling the coatings formed. Accordingly, it can also be used as film-type adhesives having heat resistance.